Seriously Jacqui they are avery famous Turkish delicacy and have been for centuries, delicious, they sell them on the streets in Istanbul, partuclarly around the Galata bridge area. I guess in the Calis area not too much pollution as Mussels like Oysters are wonderful at absorbing pollutants like heavy metals so you have to be careful around areas with polluted water, which is why I didnt eat them in Istanbul with half the Black Sea states pollution pouring out through the Bosphorous!
